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package org.pdfbox.pdmodel.encryption;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.security.AlgorithmParameterGenerator;
import java.security.AlgorithmParameters;
import java.security.GeneralSecurityException;
import java.security.KeyStoreException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.SecureRandom;
import java.security.Security;
import java.security.cert.X509Certificate;
import java.util.Iterator;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;

import org.bouncycastle.asn1.ASN1InputStream;
import org.bouncycastle.asn1.DERObject;
import org.bouncycastle.asn1.DERObjectIdentifier;
import org.bouncycastle.asn1.DEROctetString;
import org.bouncycastle.asn1.DEROutputStream;
import org.bouncycastle.asn1.DERSet;
import org.bouncycastle.asn1.cms.ContentInfo;
import org.bouncycastle.asn1.cms.EncryptedContentInfo;
import org.bouncycastle.asn1.cms.EnvelopedData;
import org.bouncycastle.asn1.cms.IssuerAndSerialNumber;
import org.bouncycastle.asn1.cms.KeyTransRecipientInfo;
import org.bouncycastle.asn1.cms.RecipientIdentifier;
import org.bouncycastle.asn1.cms.RecipientInfo;
import org.bouncycastle.asn1.pkcs.PKCSObjectIdentifiers;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.asn1.x509.TBSCertificateStructure;
import org.bouncycastle.cms.CMSEnvelopedData;
import org.bouncycastle.cms.CMSException;
import org.bouncycastle.cms.RecipientInformation;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.pdfbox.cos.COSString;
import org.pdfbox.exceptions.CryptographyException;
import org.pdfbox.pdmodel.PDDocument;

/**
 * This class implements the public key security handler 
 * described in the PDF specification.
 * 
 * @see PDF Spec 1.6 p104
 * 
 * @see PublicKeyProtectionPolicy to see how to protect document with this security handler.
 * 
 * @author Benoit Guillon (benoit.guillon@snv.jussieu.fr)
 * @version $Revision: 1.3 $
 */
public class PublicKeySecurityHandler extends SecurityHandler 
{
    
    /**
     * The filter name.
     */
    public static final String FILTER = "Adobe.PubSec";
    
    private static final String SUBFILTER = "adbe.pkcs7.s4";
    
    private PublicKeyProtectionPolicy policy = null;
    
    /**
     * Constructor.
     */
    public PublicKeySecurityHandler()
    {
    }
    
    /**
     * Constructor used for encryption.
     * 
     * @param p The protection policy.
     */
    public PublicKeySecurityHandler(PublicKeyProtectionPolicy p)
    {
        policy = p;
        this.keyLength = policy.getEncryptionKeyLength();
    }
    
    /**
     * Decrypt the document.
     * 
     * @param doc The document to decrypt.
     * @param decryptionMaterial The data used to decrypt the document.
     * 
     * @throws CryptographyException If there is an error during decryption.
     * @throws IOException If there is an error accessing data.
     */
    public void decryptDocument(PDDocument doc, DecryptionMaterial decryptionMaterial)
        throws CryptographyException, IOException
    {
        this.document = doc;
        
        PDEncryptionDictionary dictionary = doc.getEncryptionDictionary();
        
        if(dictionary.getLength() != 0)
        {
            this.keyLength = dictionary.getLength();
        }
        
        if(!(decryptionMaterial instanceof PublicKeyDecryptionMaterial))
        {
            throw new CryptographyException(
                "Provided decryption material is not compatible with the document");
        }
        
        PublicKeyDecryptionMaterial material = (PublicKeyDecryptionMaterial)decryptionMaterial;        
        
        try
        {
            boolean foundRecipient = false;            
        
            // the decrypted content of the enveloped data that match 
            // the certificate in the decryption material provided    
            byte[] envelopedData = null;            
            
            // the bytes of each recipient in the recipients array
            byte[][] recipientFieldsBytes = new byte[dictionary.getRecipientsLength()][];
            
            int recipientFieldsLength = 0;
            
            for(int i=0; i<dictionary.getRecipientsLength(); i++)
            {
                COSString recipientFieldString = dictionary.getRecipientStringAt(i);
                byte[] recipientBytes = recipientFieldString.getBytes();
                CMSEnvelopedData data = new CMSEnvelopedData(recipientBytes);
                Iterator recipCertificatesIt = data.getRecipientInfos().getRecipients().iterator();
                while(recipCertificatesIt.hasNext())
                {
                    RecipientInformation ri = 
                        (RecipientInformation)recipCertificatesIt.next();
                    // Impl: if a matching certificate was previously found it is an error, 
                    // here we just don't care about it
                    if(ri.getRID().match(material.getCertificate()) && !foundRecipient)
                    {
                        foundRecipient = true;
                        envelopedData = ri.getContent(material.getPrivateKey(), "BC");            
                    }
                }
                recipientFieldsBytes[i] = recipientBytes;
                recipientFieldsLength += recipientBytes.length;
            }
            if(!foundRecipient || envelopedData == null)
            {
                throw new CryptographyException("The certificate matches no recipient entry");
            }
            if(envelopedData.length != 24)
            {
                throw new CryptographyException("The enveloped data does not contain 24 bytes");
            }
            // now envelopedData contains:
            // - the 20 bytes seed
            // - the 4 bytes of permission for the current user                          
            
            byte[] accessBytes = new byte[4];
            System.arraycopy(envelopedData, 20, accessBytes, 0, 4);
            
            currentAccessPermission = new AccessPermission(accessBytes);
            currentAccessPermission.setReadOnly();
            
             // what we will put in the SHA1 = the seed + each byte contained in the recipients array 
            byte[] sha1Input = new byte[recipientFieldsLength + 20];
            
            // put the seed in the sha1 input
            System.arraycopy(envelopedData, 0, sha1Input, 0, 20); 
            
            // put each bytes of the recipients array in the sha1 input
            int sha1InputOffset = 20;            
            for(int i=0; i<recipientFieldsBytes.length; i++)
            {
                System.arraycopy(
                    recipientFieldsBytes[i], 0, 
                    sha1Input, sha1InputOffset, recipientFieldsBytes[i].length);
                sha1InputOffset += recipientFieldsBytes[i].length;                
            }
            
            MessageDigest md = MessageDigest.getInstance("SHA-1");            
            byte[] mdResult = md.digest(sha1Input);
            
            // we have the encryption key ...
            encryptionKey = new byte[this.keyLength/8];            
            System.arraycopy(mdResult, 0, encryptionKey, 0, this.keyLength/8);
            
            proceedDecryption();
            
            
        }
        catch(CMSException e)
        {
            throw new CryptographyException(e);
        }
        catch(KeyStoreException e)
        {
            throw new CryptographyException(e);
        }
        catch(NoSuchProviderException e)
        {
            throw new CryptographyException(e);
        }
        catch(NoSuchAlgorithmException e)
        {
            throw new CryptographyException(e);
        }
        
    }
  
    /**
     * Prepare the document for encryption.
     * 
     * @param doc The document that will be encrypted.
     * 
     * @throws CryptographyException If there is an error while encrypting.
     */
    public void prepareDocumentForEncryption(PDDocument doc) throws CryptographyException 
    {
        
        try
        {
            Security.addProvider(new BouncyCastleProvider());
            
            PDEncryptionDictionary dictionary = doc.getEncryptionDictionary();
            
            dictionary.setFilter(FILTER);
            dictionary.setLength(this.keyLength);            
            dictionary.setVersion(2);
            dictionary.setSubFilter(SUBFILTER);
            
            byte[][] recipientsField = new byte[policy.getRecipientsNumber()][];            
                        
            // create the 20 bytes seed

            byte[] seed = new byte[20];

            KeyGenerator key = KeyGenerator.getInstance("AES");            
            key.init(192, new SecureRandom());
            SecretKey sk = key.generateKey();            
            System.arraycopy(sk.getEncoded(), 0, seed, 0, 20); // create the 20 bytes seed
                
            
            Iterator it = policy.getRecipientsIterator();
            int i = 0;
            
            
            while(it.hasNext())
            {
                PublicKeyRecipient recipient = (PublicKeyRecipient)it.next();                
                X509Certificate certificate = recipient.getX509();
                int permission = recipient.getPermission().getPermissionBytesForPublicKey();
            
                byte[] pkcs7input = new byte[24];
                byte one = (byte)(permission);
                byte two = (byte)(permission >>> 8);
                byte three = (byte)(permission >>> 16);
                byte four = (byte)(permission >>> 24);
                            
                System.arraycopy(seed, 0, pkcs7input, 0, 20); // put this seed in the pkcs7 input
                                    
                pkcs7input[20] = four;
                pkcs7input[21] = three;                
                pkcs7input[22] = two;
                pkcs7input[23] = one;
                    
                DERObject obj = createDERForRecipient(pkcs7input, certificate);
                    
                ByteArrayOutputStream baos = new ByteArrayOutputStream();
                    
                DEROutputStream k = new DEROutputStream(baos);
                    
                k.writeObject(obj);
                    
                recipientsField[i] = baos.toByteArray();
                    
                i++;
            }

            dictionary.setRecipients(recipientsField);
            
            int sha1InputLength = seed.length;
            
            for(int j=0; j<dictionary.getRecipientsLength(); j++)
            {
                COSString string = dictionary.getRecipientStringAt(j);
                sha1InputLength += string.getBytes().length;
            }
                        
                        
            byte[] sha1Input = new byte[sha1InputLength];            
            
            System.arraycopy(seed, 0, sha1Input, 0, 20);
            
            int sha1InputOffset = 20;

            
            for(int j=0; j<dictionary.getRecipientsLength(); j++)
            {
                COSString string = dictionary.getRecipientStringAt(j);                
                System.arraycopy(
                    string.getBytes(), 0, 
                    sha1Input, sha1InputOffset, string.getBytes().length);                
                sha1InputOffset += string.getBytes().length;
            }            
            
            MessageDigest md = MessageDigest.getInstance("SHA-1");
            
            byte[] mdResult = md.digest(sha1Input);
            
            this.encryptionKey = new byte[this.keyLength/8];
            System.arraycopy(mdResult, 0, this.encryptionKey, 0, this.keyLength/8);
            
            doc.setEncryptionDictionary(dictionary);
            doc.getDocument().setEncryptionDictionary(dictionary.encryptionDictionary);            
            
        }
        catch(NoSuchAlgorithmException ex)
        {
            throw new CryptographyException(ex);
        }
        catch(NoSuchProviderException ex)
        {
            throw new CryptographyException(ex);
        }
        catch(Exception e)
        {
            e.printStackTrace();
            throw new CryptographyException(e);
        }
        
    }    
    
    private DERObject createDERForRecipient(byte[] in, X509Certificate cert) 
        throws IOException,  
               GeneralSecurityException 
    {
        
        String s = "1.2.840.113549.3.2";
        
        AlgorithmParameterGenerator algorithmparametergenerator = AlgorithmParameterGenerator.getInstance(s);
        AlgorithmParameters algorithmparameters = algorithmparametergenerator.generateParameters();        
        ByteArrayInputStream bytearrayinputstream = new ByteArrayInputStream(algorithmparameters.getEncoded("ASN.1"));
        ASN1InputStream asn1inputstream = new ASN1InputStream(bytearrayinputstream);
        DERObject derobject = asn1inputstream.readObject();
        KeyGenerator keygenerator = KeyGenerator.getInstance(s);
        keygenerator.init(128);
        SecretKey secretkey = keygenerator.generateKey();
        Cipher cipher = Cipher.getInstance(s);
        cipher.init(1, secretkey, algorithmparameters);
        byte[] abyte1 = cipher.doFinal(in);
        DEROctetString deroctetstring = new DEROctetString(abyte1);
        KeyTransRecipientInfo keytransrecipientinfo = computeRecipientInfo(cert, secretkey.getEncoded());
        DERSet derset = new DERSet(new RecipientInfo(keytransrecipientinfo));
        AlgorithmIdentifier algorithmidentifier = new AlgorithmIdentifier(new DERObjectIdentifier(s), derobject);
        EncryptedContentInfo encryptedcontentinfo = 
            new EncryptedContentInfo(PKCSObjectIdentifiers.data, algorithmidentifier, deroctetstring);
        EnvelopedData env = new EnvelopedData(null, derset, encryptedcontentinfo, null);
        ContentInfo contentinfo = 
            new ContentInfo(PKCSObjectIdentifiers.envelopedData, env);
        return contentinfo.getDERObject();        
    }
    
    private KeyTransRecipientInfo computeRecipientInfo(X509Certificate x509certificate, byte[] abyte0)
        throws GeneralSecurityException, IOException
    {
        ASN1InputStream asn1inputstream = 
            new ASN1InputStream(new ByteArrayInputStream(x509certificate.getTBSCertificate()));
        TBSCertificateStructure tbscertificatestructure = 
            TBSCertificateStructure.getInstance(asn1inputstream.readObject());
        AlgorithmIdentifier algorithmidentifier = tbscertificatestructure.getSubjectPublicKeyInfo().getAlgorithmId();
        IssuerAndSerialNumber issuerandserialnumber = 
            new IssuerAndSerialNumber(
                tbscertificatestructure.getIssuer(), 
                tbscertificatestructure.getSerialNumber().getValue());
        Cipher cipher = Cipher.getInstance(algorithmidentifier.getObjectId().getId());
        cipher.init(1, x509certificate.getPublicKey());
        DEROctetString deroctetstring = new DEROctetString(cipher.doFinal(abyte0));
        RecipientIdentifier recipId = new RecipientIdentifier(issuerandserialnumber);
        return new KeyTransRecipientInfo( recipId, algorithmidentifier, deroctetstring);
    }
        
}
